Normal urination and continence is dependent upon normal function of the urinary tract, kidneys and nervous system. In addition, in women, continence requires correct coaptation and urethral support. Specifically, in order for continence to be maintained, the urethra must be supported and stabilized in its normal anatomic position behind the pubic bone, adjacent to the vaginal wall. The natural support system for the female urethra is a layer of support composed of pelvic and vaginal wall tissue and ligaments, which attach to the pubic bone. Relaxation, weakening or loss of this support system results in hypermobility of the urethra and bladder to an unnaturally low position within the pelvis. This defect contributes to about 30% of incontinence in women.
One form of incontinence, referred to as stress incontinence, is an involuntary loss of urine that occurs with increased abdominal pressure such as with coughing, sneezing, laughing, or lifting. Urethral hypermobility may be a result of pregnancy (one reason why stress incontinence is common in women who have had multiple pregnancies), or may be due to pelvic prolapse. In pelvic prolapse, there is a protrusion or falling of the bladder, urethra, or rectal wall into the woman's vaginal space. Additionally, in women with low estrogen levels such as in post-menopausal females, stress incontinence is more likely to occur due to decreased vaginal muscle tone resulting from the loss of estrogen.
Approaches for treating female urinary incontinence vary and include methods directed at elevating the urethra or the bladder neck (upper region of the urethra) to return it to its normal anatomical position behind the pubic bone. These methods include needle suspension procedures and sling procedures. The needle suspension procedure is a commonly used procedure which involves placement of sutures in the support tissue (fascia) on either side of the displaced urethra and attaching these sutures to fixed sites such as bone and soft tissue. Therefore, a variety of devices have been developed to aid in the fixed attachment of the sutures to the support structures. A disadvantage with this approach, however, is that the tissue support structures being used for the urethra are themselves stretched or otherwise deficient, thereby, making them inefficient as support structures and a less effective solution.
Another approach for treating female incontinence is the sling procedure. In this procedure a sling is formed by taking a piece of human abdominal tissue (fascia) or a piece of synthetic material and using this as a platform to provide support and/or restore the urethra to its normal retropubic position. Slings made of biological tissue require either growing or harvesting autologous tissue or using processed cadaveric tissue. Therefore, these types of sling materials are sometimes undesirable in that they increase the expense, surgeon's time required and complexity of the procedure.
As an alternative to human tissue, prefabricated or synthetic slings have been developed for use in treating incontinence and are described, for example, in U.S. Pat. No. 6,042,534. These slings are said to offer improvements to the sling procedure for treating incontinence in that the synthetic slings are supplied to the physician in shapes and dimensions adapted for urethral stabilization. This eliminates the need for sizing of the sling material by the surgeon during surgery, which greatly reduces the time required for the surgical procedure.
Another example of a synthetic sling and system for use in treating incontinence is described in U.S. Pat. No. 6,039,686 issued Mar. 21, 2000 to Kovac. The sling system of Kovac involves stabilizing the urethra using a mesh sling having an innovative mesh suturing pattern that is secured in vivo by short sutures attached to the posterior/inferior (lower, back) portion of the pubic bone instead of the superior (upper) portion of the pubic bone as with other methods.
The tissue and mesh used in prior slings can be fabricated or obtained from a variety of materials and sources. There does not appear to be any attention given to configuring, creating or modifying these slings in a manner to provide optimal elongation characteristics to the support tissue. Particular elongation properties are desirable in some circumstances, such as when the amount of tension or support at the region immediately surrounding the bladder neck of the urethra is important.
Tissue ingrowth, infection resistance and capacity to erode surrounding tissue are also factors in sling designs. The specific effect of the elasticity of the sling on these factors is not known in great detail.
In view of the above, although improvements in surgical treatment of urinary incontinence have been made, there is a need to provide even more improved sling systems so as to further enhance reliability and to better respond to patient kinetics.